1. Field of the Invention
The invention pertains to a vibration damper of the type including a damping medium filled cylinder in which a piston rod carrying a working piston is guided with freedom of axial movement, the working piston dividing the cylinder into two working spaces, and a housing having first and second working chambers separated by a separating piston, the first working chamber being connected to one of the working spaces to provide amplitude selective damping as the working piston moves in cylinder.
2. Description of the Related Art
DE 10 2004 034 057 B4 and DE 10 2004 015 065 A1 describe vibration dampers with amplitude-selective damping force. Inside a housing, a separating piston, which is supported with freedom to slide back and forth and which separates two working chambers. Each working chamber has a flow connection with a single working space, where the two working spaces are separated from each other by a damping force. The piston is equipped with damping valves, where the amplitude-selective damping device with the housing and the separating piston acts hydraulically in parallel with the damping valves in question.
The separating piston has an elastomeric body, which is intended to suppress noise in the end-contact position. A seal is present between the separating piston and the inside wall to prevent leakage. A radially outer reinforcing ring gives the separating piston rigidity in the area of the seal, so that the seal is effective at all times.
The seal on the separating piston and the associated friction against the inside wall of the housing, however, can decrease to an undesirable level the sensitivity with which the amplitude-selective damping responds.
US 2005/0230202 describes a vibration damper with basically the same design. To provide the amplitude-selective damping, it has a foam body in the housing. The foam body fills the entire volume of the housing. When the piston rod moves, there is no flow between the working spaces of the vibration damper; instead, there is only a one-sided compression of the foam body.
At high piston rod speeds, the jet of damping medium coming from the flow connection and acting on the foam body has a highly abrasive effect, so that separated particles can enter the damping valves and interfere with their proper operation.